A signal is commonly transferred through a transmission line which may be a printed circuit board trace or a metal line. Such a signal is generally transferred in one of a voltage mode or a current mode. For transmission of digital data in the voltage mode, a signal received with a voltage level in a range of from about 2.7 Volts to 3.3 Volts is interpreted as having a logic high state. Alternatively, a signal received with a voltage level in a range of from about 0 Volts to 0.6 Volts is interpreted as having a logic low state. However, resistive-capacitive delays during data transmission may result in signal distortion in the voltage mode, especially during high speed operation.
In contrast for the current mode, current levels are used instead for indicating logic state. A signal received with a current level in a range of from about 17 milli-Amps to 23 milli-Amps is interpreted as having a logic high state. Alternatively, a signal received with a current level in a range of from about 0 milli-Amps to 6 milli-Amps is interpreted as having a logic low state. Resistive-capacitive delay during signal transmission does not affect current level such that data transmission in the current mode is not as sensitive to the resistive-capacitive delay.
For data transmission in pseudo-differential current mode, a transmitter transfers a reference current and a data current. The receiver then determines the logic state by comparing the reference current and the data current. For enhanced operation, the noise in the reference current and the data current are desired to be equalized. Such equalized noise may be canceled in the difference between the reference current and the data current. In addition for improved operation, a pseudo-differential current mode receiver is desired to have low input impedance and high output impedance.